[General:005]: Diagram reconciliation

The sequence diagram editor SHALL reconciliate the graphical elements with the uml elements.
- Graphical elements (notation views) without elements should be removed.
- For UML elements without a graphical representation, a graphical representation SHALL be added at the right place using the principles described in #23.
- Displaced graphical elements SHALL be removed and new ones added at the right position using the principles described in #23. If for some reason the reconciliation cannot be achieved, a notification should be display to the user asking for recreation of the whole diagram, by deleting it and recreate it again.